Magnetic well logging



Jan. 11, 1944. J, c. ARNOLD MAGNETIC WELL LOGGING Filed Oct. 19, 1940 2Sheets-Sheet 1 RECORDING METER AMPLIFIER INVENTOR f/15s TAE/v0.40

ATTORNEY M rllm 1.

Jan. 11, 1944. J c. ARNOLD '2,338,991

' MAGNETIC WELL LOGGING Filed oct. 19, 1940 2 sheets-sheet 2 E625ATTORNEY complicated Patented Jan. 11, 1944 MAGNETIC WELL LOGGIN G JamesC. Arnold, Los Angeles, Calit, assigner to Lane-Wells Company, LosAngeles, Calif., a

corporation of Delaware Application October 19, 1940, Serial No. 361,947

4 Claims.

My invention relates to magnetic well logging for the purpose ofidentifying formation confronting a well bore by its magneticlproperties. During the process of sedimentation of the various stratawhich are penetrated by an oil well bore, magnetic particles containedin the strata tend to orient themselves with respect to the magnetic eldof the earth. The direction and intensity of the earths magnetic eldthrough the ages has varied through extreme ranges. sedimentation of thevarious strata has occurred at intervals of many million years, so thatthe magnetic axes of the various strata have varied accordingly. Alsothe amount of iron 0r other magnetic material within the strata differsand the various formations tend to inuence or affect the now existingearths magnetic field. All of these factors tend to introduce anomaliesand variations in the magnetic properties of the formation confronting awell bore. By detecting and correlating records taken from differentwells in a given eld it is possible to identify various formations.Accordingly, among the objects of my invention are:

First, to provide, in general, a method and apparatus for recordinganomalies or variations in the magnetic properties of formationsconfronting a well bore;

Second, to provide a method and apparatus of this character which isinfluenced to a minimum extent by the azimuthal direction of the earthsmagnetic field so that the instrument may rotate considerably during itsmovement through the well bore without influencing its operation;

Third, to provide a method and means of this character whereby themagnetic forces being measured are concentrated so as to increase the yeffect of the magnetic field upon the instrument;

Sixth, to provide an apparatus of this char-l acter in which the recordis made within the instrument itself, thereby eliminating the need ofsurface-recording apparatus or transmission means with the attendantdifficulties of producing a record which is free of spurious indicationsintroduced when attempting to transmit the signals obtained;

'ini

Seventh, to provide an apparatus which, in its one form, employs amagnetizable Wire which is advanced through the instrument in proportionto the movement of the instrument in the well bore, so that the wireitself contains the record of the magnetic anomalies encountered and maybe at any subsequent time decoded by running the Wire through a suitabledecoding machine and recording apparatus; and

Eighth, to provide another form oi apparatus which produces a recordwithin the instrument on photographic lrn, which film may serve directlyas a record chart.

With the above and other objects in view, as may appear hereinafter,reference is directed to the drawings, in which:

Figures 1 through 4 illustrate one form of my invention; Figure 1 is apartial elevational, partial diagrammatical view of my apparatus, theform which employs a magnetizable wire;

Figure 2 is an enlarged, longitudinal, fragmentary sectional View of theupper portion of the apparatus, viewed in the same direction as Figure1;

Figure 3 is a similar longitudinal sectional view of the lower portionof the apparatus, continuing from Figure 2 and likewise viewed in thesame direction as Figure l; and

Figure 4 is a diagrammatical view of the decoding apparatus fortranslating the record made on the magnetic wire to a record chart.

Figures 5 through 9 illustrate a modified form of my apparatus in whichthe record is made photographically:

Figure 5 is a longitudinal sectional View of the lower portion of theapparatus;

Figure 6 is a transverse sectional View taken through 6-6 of Figure 5;

Figure 7 is a continuation of Figure 5; v

Figure 8 is a diagrammatical View of the apparatus; and

Figure 9 is a representation of a typical record obtained from themodified apparatus.

Reference is rst directed to Figures 1 through 4: In the structure hereshown the instrument is lowered on a cable I, preferably carrying iveconductors. The cable passes around a sheave 2 and winds upon a hoistdrum 3. The conductors of the cable are connected to a motor unit 4driven from the sheave 3. This type of motor unit is commercially knownas a Selsyn. motor unit and is adapted to cause synchronous movement ofa like unit. The lower end of the cable l is provided with a, cable head5 which is joined to a tubular case 6 in the upper end oi the case Gthere is mounted a motor unit l which a cou'ipanion to the motor unitli. A. frame structure S is provided een low the motor unit E whichsupoorts a spool c adapted to receive a niasnetizable it. Below thespool il the roaoroetitable extends over a feeding wheel il and is heldthereon by idler wheels A cross @Si provided at upper end oi the iframeil is driven by beveled gears from the motor unit cross shait isconnected by sproclret and che-in roeans if; to th wheel il and by suitbie friction drive means 'i to the spool Below the iranien-forli', ilthe ease il is provided with a pair or concentrating bars extend'longitudinally alone diainetricaliy op'- posite sides of the caseoverlap only slightly at their adjacent ends. i their overlapping endsthey are provided l:tuned pole pieces l l. The pole pieces terminate inclose proximity to each other and the rnagnetizable wire lll) is adaptedto pass therebetween. concentrating bars lil are tor-ined o materialhaving high magnetic permeability such as a material known commerciallyas inennalloy in order to facilitate mounting within the case d they mayhave at their extended ends die-cast discs l and at their central oroverlapping ends the pole pieces may he molded or die-cast within acentrai disc le, the discs lil and i9, oi' course, being 'formed oinonnniaenetie material such as eine or the like. rlihe lower end thecase receives a fitting 2d which carries a spool support ill in the formoi a yoire. e spool is mounted in the spool support and magnetioalolewire from the spool is adapted to pass over an idler wheel carried bythe support.

The support 2i and trame d may be provided with guide tubes 2li whichmay entend through the end discs i@ into sockets formed in the cen 'traldisc l@ which register with a hole in the disc to accommodate themagnetizable wire. IThus the wire may be readily threaded from the spool22 upwardly through the guide tubes to the receiving spool il. il. capnts over` the lower end of the fitting 2li to enclose the spoolOperation of apparatus as shown in Figures i, 2 and 3, is as i'ollows:The instrument is moved alone` a well-bore and the motors are caused tooperate in synchronism so that for every foot of travel of theapparatus, a corresponding length of wire is fed past the pole pieces.The magnetizable wire may be extremely small and, consequentlyy a largequantity, in iact, several thousand feet, may be wound on spools orquite small diameter. Thus it is possible that the record bear a directratio to the depth of well being surveyed, that is, the magnetizablewire being caused to move upwardly at the same rate the instrument islowered so that there is a one to one ration. Actually, however, a fewinches of wire may represent a hundred feet of well-bore; this may beacomplished by simply moving the Wire at a slower speed.

In this connection, it should be noted that it is not necessary for theWire to move continuously, but it may be moved in steps; that is, aseries of records taken at different points along the well-bore may bemade instead of a continuous record, in which case the magnetic wirewould be caused to advance in steps much in the manner of thenlm-controlled mechanism to be described hereinafter.

After the record has been impressed upon the The bars assasoi wire andthe instrument removed from the wellbore the wire is unwound trom thespool S onto another spool ill, and caused to pass through a piclruupunit The pick-up unit is electrically connected through an amplifier d3to recordine meter which is provided with a stylus or similar recordingelement 3E adapted to move in accordance with the change in magneticintensity on the wire and record the same on a moving chart la all asshown dagranimatically in Figure Ei 'the wire has been caused to advancestep by step, rather than continuously', the decodingn or translating`apparatus shown in mgure l would likewise be provided with means forstep-'brestois movement of the wire.

Reference is now directed Figures t3 through e: in this construction theapparatus contained in a tubular oase di covered at its lower end by acap 32., Within the case are secured a pair of concentrating bars 43arranged as in the rst described structure with one bar extending upwardly and the other downwardly, and on di1 ametrically opposite sidesof the case, the adjacent ends oi the concentrating hars overlappingslightly and being provided with pole pieces M. The pole pieces aresimilar to those used in milliainmeters, that they denne a cylindricalopenin wlich is mounted a meter coil d5. rEhe pole piecesare encased ina suitable molded body alli of nommagnetic material. The body 4t carries a framework ll which supports the meter coil d. Extending rom themeter coil @l5 is a pointer 6l@ which is directed upward. The axis ofcoil is at right angles to the axis of the case lll so the pointerextends longitudinally and its upper end is bent horizontally over ascale 49 which may be formed on a part of the molded body dll at itsupper end.

Alone' the side oi' the lower concentrating bar dil is a batterycompartment lill containing batteries di. ported a i'rarne which carriesa series of electric lights 53 connected with the battery for thepurpose of illuminating the scale and pointer. The meter coll islikewise connected with the batteries.

Within the case above the upper concentrating bar 33 is mounted a cameramechanism ill. The carriera mechanism comprises a :frame 62 whichsupports nlm reels 63 and 6d between which is adapted to pass aphotographic lm $5. The film passes from the upper reel down along oneside of the frame and across the lower end, that is, across the aperture66, being held in proper position by guide rollers B7. After passingaround the guide rollers the lm is directed upwardly around a drivewheel 68 to the reel 64. The drive wheel 68 is actuated by a gear train69 which in turn is actuated by a drive ratchet lll. The ratchet lll isoperated by a bar 'H which is mounted along the side of the frame 62.The bar is adapted to reciprocate and is provided with a pawl l2. Theoperating bar H extends to the upper end of the frame 62 and isattached'to an armature 73, which cooperates .with a solenoid lili. Thearmature causes upward movement of the operating arm while a spring 'l5urges the arm downwardly. The ratchet and pawl are so arranged that thefilm does not advance during 'upward movement of the operating bar, butonly with downward movement of the bar. Below the aperture 65 there isprovided a suitable shutter lt which is actuated by a lever l1 extendingupwardly along the side of the frame and positioned so as to be engagedby a lug -l extending from Above the pole pieces fifi there is sup- Ithe operating bar 1|. The shutter is caused to operate during upwardmovement of the operating bar, so that with each operation of the barthe shutter is operated and then the film is mo-ved into a new position.Extending from the camera mechanism is a sighting tube 'I9 containing asuitable lens system and terminating in proximity to the scale 49 sothat the scale and pointer may be photographed. The camera mechanism isso positioned that the pointer 48 moves crosswise with respect to thefilm, and only a very narrow strip of film need be provided for eachrecord, as shown in Figure 9 in which 49a represents the photograph ofscale 49 and 48a represents the photograph of the pointer I8.

The solenoid is electrically connected through a single conductor cable80 to a switch 8| and battery 82. The switch 8| is cam-actuatedperiodically by a cam wheel 83 which is driven by a transmission 84suitably driven, as by a Selsyn drive 85, from a sheave wheel 86, overwhich the cable passes. Thus the camera mechanism is caused to take apicture and move the nlm for each predetermined length of cable travel;for example, a picture may be taken, one each footl or each two feet, orve feet, depending upon the detail it is desired to obtain in therecord.

Operation of the apparatus shown in Figures to 9 is as follows: Theinstrument is preferably moved at a uniform rate and the meter,represented by the coil and pointer, is preferably dampened in anyconventional manner so that ordinary shaking of the instrument will notun* duly affect the meter. In an instrument no larger than the drawing,as actually shown, several hundred inches of film may be carried and therecords may be placed as close as twenty-live to the inch, thus if therecords are made at twofoot intervals some iive thousand feet of wellbore may be recorded. Of course, it is not necessary to investigate theentire well. but only that portion in which it is likely that oil may befound.

In both constructions the concentrating bars are formed of highlypermeable material and have the effect of concentrating the magneticfield embraced between the extremities of the bars at the meter or thegap through which the magnetic wire passes. The dip of the magneticfield, however, has an eflect that may be largely compensated for ordiscounted for the reason. that, normally, the dip of the earthsmagnetic field is substantially constant, assuming, of course, that thewell is straight. Inasmuch as the present practice is to drill a wellwithin rather close tolerances, in most instances no appreciable errorwill arise by reason oi' change in the angle of the well bore.Furthermore, should it be desired to investigate a well bore that is notstraight, a survey of the well bore may be made to determine its courseand such a record be used to determine the correction factors thatshould be applied to the record obtained by my apparatus.

The longer the concentrating bars the stronger will be the eiect;however, this effect will be the average of the magnetic eld between theextremities of the concentrating bars. Consequently, the length of theconcentrating bars should be less than the probable minimum thickness ofthe strata to be investigated.

Various changes and alternate arrangements may be made Within the scopeof the appended claims, in which it is my intention to claim all noveltyinherent in the invention as broadly as the prior art permits.

I claim:

l. A method of identifying formation confronting a well bore,characterized by: concentrating the magnetic field present inpredetermined sections of a well bore upon corresponding sections of amagnetizable wire; removing the wire from the well bore; and recordingthe variations in magnetic condition of said wire along its length.

2. An apparatus for investigating a well bore, comprising: amagnetizable wire; a case therefor adapted to be lowered into a wellbore; reels for said wire in said case; means for advancing said wirefrom one reel to the other; a control for said means coordinated withmovement of said case through a well bore; and means for concentratingthe magnetic field in the well bore on said wire, whereby a magneticimpression of said field is formed thereon.

3. 'I'he combination with the apparatus set forth in claim 2 of arecording means including a pick-up unit adapted, when moved along saidwire, to detect the magnetic impressions thereon.

4. An apparatus for logging well bores, comprising: a housing adapted tobe lowered into a well bore; highly permeable elements arrangedlongitudinally therein; coacting pole pieces associated with saidpermeable elements and defining therebetween a gap, the permeableelements and pole pieces being so arranged that the magnetic 'fieldembraced by said elements is concentrated across said gap: amagnetizable wire in said gap; means for moving the wire past the polepieces; means for moving said housing along a well bore;

'and a device for correlating the movements of said means.

JAMES C. ARNOLD.

